In a conventional capacitor on plug (COP) device 1, such as the FeRAM shown in FIG. 1, contact plugs 2 are often used as vertical interconnects between metal lines in multilevel interconnect schemes. The contact plugs 2, which are typically formed of tungsten, pass through apertures in the substrate 4 of the device. The device 1 also includes a layer of ferroelectric material 6, such as PZT, with a top electrode 7 above the ferroelectric layer 6 and a bottom electrode 8 below the ferroelectric layer 6. A barrier layer 9, which is typically iridium (Ir) or titanium (Ti) based, is often positioned between the bottom electrode 8 (BE) and the substrate 4. The barrier layer 9 is deposited on top of the contact plugs 2 to block oxygen from causing damage when oxygen diffuses to the plugs 2. The barrier layer 9 improves contact resistance between the bottom electrode 8 and the contact plugs 2 and it also acts as a glue layer to improve adhesion of the bottom electrode 8 to the substrate 4. The apertures in the substrate 4 through which the contact plugs 2 extend are lined with the glue layer 9.
An oxygen barrier layer 10 of, for example, aluminium oxide, is typically deposited around the finished capacitor to reduce the amount of oxygen seeping into the capacitor along the glue layer 9 and oxidising the glue layer 9. This is most likely to occur during processing, particularly during the process of recovery annealing in an oxygen atmosphere, when oxygen may seep through faults in the oxygen barrier layer 10 which, if it reaches the plugs 2, may damage the contact between the bottom electrode 8 and the plugs 2 causing failure of the device.
In view of the foregoing problems with conventional processes and devices, a need exists for a method for inhibiting oxidation of the plug during the manufacture of a capacitor.